The present invention relates to a plastic scrap extruding apparatus, which is a component of a plastic pellet forming equipment for reproducing plastic pellets from plastic scraps, e.g., sprues and runners formed by injection molding, fins formed by blow molding, and which is capable of plasticizing and extruding the plasticized scraps.
Conventionally, in injection molding plants, plastic scraps, e.g., sprues, runners, fins, are crushed, and the crushed materials are mixed with new materials to reuse. Molding must be stably performed with using the mixed materials, but using the mixed materials causes some problems, e.g., forming powders of the crushed materials, reproduced pellets having different sizes, non-uniform mixture of the reproduced pellets and new pellets. To solve the above described problems, the reproduced pellets whose size and shape are equal to those of new pellets must be produced by a plastic pellet forming equipment, and a compact pellet forming equipment is required.
Conventional pellet forming equipments have following problems, so they have not been popularized.
Firstly, a general extruding apparatus of the conventional pellet forming equipment has a material tank, which is provided in a material supplying section. In case of using this extruding apparatus of the pellet forming equipment, plastic scraps which have been discharged from a molding machine at regular intervals are once crushed by a crusher, and then the crushed scraps are transferred to the material tank as crushed materials. Therefore, the transferring step is troublesome, and there is a possibility that foreign matters invade into the crushed materials in the transferring step.
The crushed materials are tended to be left in the air, so some crushed materials absorb moisture from the air. If the crushed materials absorb moisture, the crushed materials cannot be used, for forming pellets, without being dried.
Further, it is required that the crushed materials have the size and shape which can be received by an extruding screw. But, the crusher is designed on the basis that the crushed materials are mixed with new materials. Therefore, the crusher has a complex structure, and a production cost of the crusher must be increased.
To solve the above described problems, a new extruding apparatus was proposed (see page 1 of Japanese Laid-open Patent Publication No. 2009-39871). In the apparatus, the step of crushing plastic scraps, which have been discharged from a molding machine, is omitted, the plastic scraps are crushed by a drawing section of an extruding screw, and the crushed scraps are conveyed to a plasticizing section of the extruding screw.
However, in the extruding apparatus, treatable scraps are limited to small scraps, e.g., sprues formed while producing CDs and DVDs, whose size is nearly equal to an outer diameter of the extruding screw. Therefore, general large plastic scraps cannot be treated.
Further, another new extruding apparatus, which can treat large scraps, was proposed (see page 1 of Japanese Translation PCT Publication No. 07-507730). In the apparatus, a two-shaft shredder is assembled so as to crush large plastic scraps.
However, in the apparatus, a conventional crusher is merely assembled to a material supply section of the conventional extruding apparatus. The extruding screw and the crusher are driven by separate driving mechanisms, and a structure of a rotary blade is complicated. Further, a large amount of scraps can be effectively treated at a time, but scraps, which have been discharged from a molding machine at regular time intervals (e.g., 20-30 seconds mostly), are treated one by one. The structure of the apparatus is complicated and a production cost thereof is high in regard to the function.
Namely, the problems of the conventional extruding apparatuses are that plastic materials produced by crushing plastic scraps cannot be suitably sent to a heating cylinder, that the structures are complicated and that their production costs must be high.